Magnetic array sensor circuit having offset variation reduction circuit

ABSTRACT

A magnetic array sensor circuit to process an output from a magnetic sensor array including a plurality of magnetic sensor elements arranged in an array. The circuit includes a regulating circuit to reduce an offset variation of the output from the magnetic sensor elements arranged in the array. The regulating circuit includes a control circuit to operate the magnetic sensor element in a linear region. The control circuit includes a reference sensor element in the form of the magnetic sensor element short-circuited between two output terminals, a storage element to store a reference offset value read out from the reference sensor element, and a subtraction circuit to subtract the stored reference offset value from an output of the other magnetic sensor elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims priority to U.S. applicationSer. No. 11/792,814, filed Jun. 12, 2007, which in turn claims thebenefit of International Application No. PCT/JP2005/022334 filed Dec. 6,2005, and Japanese Application Nos. 2004-361740 filed Dec. 14, 2004,2005-019641 filed Jan. 27, 2005 and 2005-167127 filed Jun. 7, 2005, thedisclosures of which are hereby incorporated herein by reference intheir entirety.

BACKGROUND

1. Field

The present invention relates to a rotation detecting apparatus fordetecting the rotation of various machines and equipments such as, forexample, for detecting the rotation for controlling rotation of acompact motor, or for detecting the rotation for detecting the positionwithin a business equipment, and also to a bearing assembly equippedwith such rotation detecting apparatus.

2. Description of the Related Art

Taking advantage of the compactness and the easiness of assemblage, abearing assembly having a rotation sensor built therein has hithertobeen suggested. One example of such bearing assembly is shown in FIG.29. In this example, a rotating ring 52 of a rolling bearing assembly 51is fixed with a member including a magnetic encoder 54 in the form ofrubber magnets having a plurality of alternating magnetic poles N and Sdeployed in a circumferential direction thereof, and a stationary ring53 is fixed with a member including a magnetic sensor 55 such as, forexample a Hall element or the like so that rotation pulse signals and/ordirection of rotation can be obtained.

However, in the structure in which the magnetic encoder 54 is providedin the manner as hereinabove described, in the case of a small diameterbearing, which is a rolling bearing assembly of a small size, problemshave been recognized in that it is difficult to allow the magneticsensor 55 to be accommodated within the outer diametric size of thestationary ring 53 and, also, to detect the rotation angle with highprecision enough to secure the number of rotation pulses that is equalto or greater than 500 per each complete rotation.

In view of the foregoing, as a rotational angle detecting device capableof being incorporated in a compact machine and also cable of providingan output descriptive of the rotation angle with high precision, adevice utilizing a sensor array has been suggested. (See, for example,the Japanese Laid-open Patent Publication No. 2003-148999 published May21, 2003.) Such device is of a structure, in which a sensor arraycomprised of a plurality of magnetic sensor elements is integrated on asensor chip together with a signal amplifier circuit, ananalog-to-digital (ND) converter circuit and a digital signal processingcircuit, which sensor chip is in turn arranged in face-to-face relationto a magnet head mounted on a rotating member. It is the principle ofthis method that the magnetic sensor array detects a distribution ofmagnetic fields generated by the magnetic head arranged in face-to-facerelation with the sensor chip so that the rotation angle of the magnetcan be detected from this distribution. However, in the case of thisconstruction, in a semiconductor circuit, it is unavoidable for circuitelements, integrated on a silicon chip, to result in variation incharacteristic and offset variations of the sensor elements tend tooccur even in the magnetic sensor array, thus constituting a cause ofdegradation of the angle detecting precision.

As an improvement to the Japanese Laid-open Patent Publication No.2003-148999, it has been suggested to arrange the magnetic sensorelements of the sensor array in parallel relation to each other in anattempt to reduce the offset variations for the purpose of reducing thedegradation of the angle detecting precision. (See, for example, theJapanese Laid-open Patent Publication No. 2004-037133, published Feb. 5,2004.) However, even though the magnetic sensor elements are arranged inparallel relation to each other, the residual offset variation stillaffects the angle detection.

For the magnetic sensor elements referred to above, MAGFET elements aregenerally utilized, each of which has such a characteristic that whenthe element is subjected to a vertically acting magnetic field, anon-equilibrium occurs in electric currents flowing across two drainterminals thereof enough to provide a current difference that representsa magnetic signal desired to be detected. However, the currentdifference generated from the magnetic sensor element is so considerablysmall as to require amplification thereof.

The magnetic detecting circuit, in which the magnetic sensor elements,i.e., MAGFET elements of the kind discussed above are employed, isreported by Shen-luan Liu, Jian-Fan Wei and Guo-Ming Sung in their“SPICE Macro Model for MAGFET and its Applications”, IEEE Trans.Circuits and Systems II, Analog and Digital Signal Processing, vol. 46,4, 1999, (which is referred to as the non-Patent Document 1). Accordingto this non-Patent Document 1, the current obtained from the terminalsof the sensor element is converted into a current difference, which isin turn converted into a voltage signal by the use of an OP amplifier.

However, the circuit disclosed in the non-Patent Document 1 referred toabove handles signals on a single-ended system and is thereforesusceptible to influence brought about by noises, as well as tends toresult in an insufficient amplification factor when the currentdifference is small. In view of this, the rotation detecting apparatusdisclosed in the non-Patent Document 1 referred to above requires thefollowing to be satisfied.

Where a signal from the sensor array is converted into a digital signalin order to calculate the angle, the sensor signal has to be amplifiedto an amplitude of at least about 1 to 2 volts before it is supplied toan analog-to-digital (ND) converter. Therefore, a circuit of a structureeffective to convert it to a voltage with sufficient amplificationfactor and operating speed is necessary, resulting in increase of theelectric power consumption.

In addition, as a method for canceling the offset of the magnetic sensorelements, the method is known in which the elements are connectedparallel to each other, as FIG. 30 shows one example thereof. In theexample shown in FIG. 30, two elements 45 a and 45 b each having twodrain terminals D1 and D2 are connected in such a manner that the samedrain terminals D1 of those elements 45 a and 45 b are connectedtogether and the same drain terminals D2 of those elements 45 a and 45 bare similarly connected together, with connection lines between thedrain terminals D1 and between the drain terminals D2 crossing relativeto each other.

Those drain currents between the two magnetic sensor elements 45 a and45 b, formed on a silicon wafer in juxtaposed relation to each other,are considered ideal if they have an equal amount in the absence ofmagnetic fields. However, a cant component will occur depending on themanufacturing process, which can result in an offset signal.Specifically, in the presence of this cant component in, for example, adirection rightwards as shown by the arrow A, in each of the magneticsensor elements 45 a and 45 b the current will tend to flow rightwardsas shown by the respective arrows a and b in FIG. 30. The method inwhich the drain terminals are cross-connected in the manner shown inFIG. 30 is effective to counterbalance the offset signals occurring inthose two sensor elements 45 a and 45 b.

However, even where the magnetic sensor elements 45 a and 45 b areconnected parallel to each other as in the example shown in FIG. 30,variation of the residual offset unavoidably adversely affects theprecision of angle detection. In particular, in the case where themagnetic sensor elements used is of a native substrate type, aconsiderable piezoresistive effect brought about by a warp of thesilicon chip causes a problem in that the offset of the sensors changesconsiderably.

It is to be noted that studies on the piezoresistive effect resultingfrom the warp of the silicon wafer is reported by Yozo Kanda in his “AGraphical Representation of the Piezoresistance Coefficients inSilicon”, IEEE Trans. Electron Device, vol. ED-29, No. 1, January 1982,which is referred to as a non-Patent Document 2, and Jefferey C. Suhlingin his “Silicon Piezoresistive Stress Sensors and Their Application inElectronic Packaging”, IEEE Sensors Journal, vol. 1, No. 1, 2001, whichis referred to as a non-Patent Document 3. The method of reducing theinfluence brought about by stresses in Hall elements is reported by, forexample, R. Steiner, et al. in their “Offset Reduction in Hall Devicesby Continuous Spinning Current Method”, Sensors and Actuators, A66, pp.167-172, 1998, which is referred to as a non-Patent Document 4.

Specifically, in the sensor element formed in a silicon wafer 40 shownin FIG. 31, the offset component brought about by the piezoresistiveeffect is caused mainly by a change in resistivity in a 45° orientationrelative to the sensor element (according to the non-Patent Document 2).The piezoresistive effect in such case is a phenomenon, in which theelectric resistivity in each of X1 and X2 directions of the wafer 40shown in FIG. 31 changes depending on the stress condition loaded on thewafer 40.

In the circuit configuration in which the magnetic sensor elements areconnected parallel as shown in FIG. 30, influence brought about by thestress (shown by S in FIG. 32A) in the silicon chip appears, as shown inFIG. 32A, as a change of the electric resistivity in a direction 45°angled relative to the sensor elements 45 a and 45 b. Accordingly, theoffsets appearing in those two sensor elements 45 a and 45 b assume thesame polarity and are not counterbalanced in this connection. In otherwords, in FIG. 32A, the resistivity in the rightwardly upward direction(the leftwardly downward direction) becomes lower than the resistivityin a direction perpendicular thereto and, consequently, an imbalancedcurrent flow occurs inside the sensor elements 45 a and 45 b as shown bythe arrows a and b. FIG. 32B illustrates a condition in which a magneticfield Bz is applied while in a condition shown in FIG. 32A. The sensorsignal in such case ideally represents an output proportional to theintensity of the magnetic field, but represents a signal superimposedwith the stress induced offset.

Also, it has been suggested to determine the rotation angle of themagnet based on an output of the magnetic sensor array. (See, forexample, the Japanese Laid-open Patent Publications No. 2004-037133 andNo. 2005-043070 published Feb. 17, 2005.) Those publications suggest arotation detecting device which includes a sensor unit in the form of asensor array composed of a plurality of arranged magnetic sensorelements and integrated on a semiconductor chip together with a signalamplifying circuit, an A/D converting circuit and a digital signalprocessing circuit. However, those publications are silent as to aspecific type of the magnetic sensor elements.

Xinyu Zheng and Suzhi Wu disclose, in their “General Characteristics andCurrent Output Mode of a MOS Magnetic Field Sensor”, Sensors andActuators, A28 (1991), pp-5, which is referred to as a non-PatentDocument 5, the fundamental characteristics of the magnetic sensorelement MAGFET and indicate the presence of a certain reduction inmagnetic sensitivity during the operation at a linear region. However,nothing is mentioned of the offset variation.

James J. Clark has suggested, in his “Split-drain MOSFET Magnetic SensorArrays”, Sensors and Actuators, A24 (1990), pp-107-116, which isreferred to as a non-Patent Document 6, a method in which the magneticsensor elements MAGFETs are arranged in a matrix pattern to detect adistribution of magnetic fields. He has also used a read-out circuitbased on a simple voltage converting circuit and has described theoffset variation of the sensor output being considerable.

SUMMARY

In view of the foregoing, an object of the present invention is toprovide a rotation detecting apparatus capable of increasing the angledetecting accuracy with a minimized power consumption and without beingaffected by an offset signal resulting from strains occurring in thesilicon chip and, also, a bearing assembly equipped with such rotationdetecting apparatus.

Another object of the present invention is to provide a magnetic arraysensor circuit capable of performing highly precise detection with aminimized offset variation occurring in the magnetic sensor elements andalso capable of increasing the quality of an output signal from thesensor array.

The rotation detecting apparatus according to one aspect of the presentinvention includes a magnetic sensor array including a plurality ofcombined sensor element groups, each group including four sensorelements, the four sensor elements of each combined sensor element groupbeing so arranged as to be oriented vertically and horizontally in fourdirections and connected parallel to each other; and a magnet rotatablein face-to-face relation with the magnetic sensor array.

According to this construction, since the four sensor elements are soarranged as to be oriented vertically and horizontally in fourdirections and connected parallel to each other, the sensor elements areoriented displaced 90° relative to each other. In those sensor elementsso displaced 90° relative to each other, the effect of stresses isreversed. For this reason, when the four sensor elements are so arrangedas to be oriented vertically and horizontally in four directions and areconnected parallel to each other to form a respective combined sensorelement group, the offset signal from the sensor elements resulting fromwarping of the semiconductor chip can be reduced in a magnetic signaloutputted from the magnetic sensor array. When the offset signalreduces, the angle detecting accuracy of the rotation detectingapparatus increases and the resolution and the accuracy as a rotaryencoder can be increased. In this construction, there is no need tochange the process of manufacturing of the sensor element in an attemptto reduce the offset signal and, therefore, no cost will increase.

In the present invention, the four sensor elements of each combinedsensor element group may be arranged in a cruciform pattern. Thecruciform arrangement of the four sensor elements is advantageous inthat the pattern of connecting wirings used to connect the sensorelements together can be shortened and simplified.

The four sensor elements of each combined sensor element group may bearranged dispersed. “Arranged dispersed” means that the sensor elementsare dispersed without respective drain terminals thereof concentrated inone area. In other words, the sensor elements may be arranged in a lineor a plurality of lines.

Even when the dispersed arrangement is employed, the effect of reducingthe offset, which is substantially similar to that obtained when thesensor elements are arranged in the cruciform pattern, can be obtained.Where the dispersed arrangement is employed, the sensor elements can beflexibly arranged and can be efficiently arranged so that formation ofunnecessary areas in the substrate can be minimized.

In the present invention, connection between the sensor element,oriented vertically, and the sensor elements, oriented horizontally, maybe provided in two modes. Those two modes of connection include a firstconnection mode for detecting a magnetic signal and a second connectionmode for detecting a stress signal.

When the two modes of connection is employed, by selectively using onlyan output from the magnetic sensor array held in either one of theconnection modes, one of the magnetic signal and the stress signal isselectively detected so that one of a rotary sensor and a stress sensorcan be selectively used.

Where the two connection modes are employed as described above, aconnection mode selecting unit may be employed for selecting one of thetwo modes of connection. The connection mode selecting unit makes useof, for example, a predetermined signal applied from an external part toselect the particular connection mode. In such case, the two connectionmodes include a first connection mode for detecting the magnetic signaland a second connection mode for detecting the stress. Thus, the use ofthe connection mode selecting unit is effective to facilitate selectionof one of the two connection modes from the external circuit and, also,to allow the only magnetic sensor array to be used selectively as one ofthe rotary sensor and the stress sensor one at a time.

A bearing assembly equipped with the rotation detecting apparatusaccording to the present invention makes use of the rotation detectingapparatus according to the foregoing first aspect of the presentinvention. In this bearing assembly, the magnetic sensor array isprovided in a stationary raceway member and the magnet is provided in arotating raceway member.

According to this construction, by integrating the rotation detectingapparatus with the rolling bearing assembly, not only can the number ofcomponent parts of the machine or equipment that utilizes the bearingassembly and the number of manufacturing steps be reduced, but alsocompactization can be achieved. In such case, since the rotationdetecting apparatus is compact in size and can provide the rotationangle output with high precision, a satisfactory rotation angle outputcan be obtained even in a small sized bearing assembly such as, forexample, a small diameter bearing.

The rotation detecting apparatus according to a second aspect of thepresent invention includes a magnetic sensor array including a pluralityof sensor elements, a magnetic generating element rotatable inface-to-face relation with the magnetic sensor array and having ananisotropy in a direction circumferentially about an axis of rotationthereof, and a read-out circuit for sequentially selecting and driving aplurality of the sensor elements forming the magnetic sensor array,extracting a signal component from an electric current flowing thesensor element, converting it into a voltage and reading the voltage.According to this construction, since the plural magnetic sensorelements forming the magnetic sensor array are sequentially selected andthe signal is read out by the read-out circuit, the amount of anelectric current to be supplied to the sensor arrays suffices to be thatrequired by one sensor element. For this reason, a large detectionsignal can be outputted with a minimized electric power consumption.

In the present invention, the read-out circuit for converting into andread out the voltage may have a circuit configuration constructed of aswitched-current system for extracting a differential current component.In the case of this construction, change of the minute sensor currentgenerated by external magnetic fields can be extracted leaving only thedifferential current component.

The read-out circuit for converting into and read out the voltage mayhave a circuit configuration constructed of a current mirror system forextracting a differential current component. Even in the case of thisconstruction, change of the minute sensor current generated by externalmagnetic fields can be extracted leaving only the differential currentcomponent.

The read-out circuit for converting into and read out the voltage mayinclude an integrating circuit utilizing a capacitor, the integratingcircuit being operable to convert the differential current component,which is a signal component extracted from the electric current flowing,into a voltage. In the case of this construction, the voltage signal ofa sufficient amplitude necessary for the A/D conversion and the signalprocessing in the subsequent stage can be obtained. In addition, byproperly setting the capacitance of the capacitor of the currentintegrating circuit, it is possible to achieve the conversion into thelarge voltage signal in an extremely short time of charging and thesensor signal read-out circuit having a high speed and a sufficientamplification factor can be constructed.

The magnetic array sensor circuit of the present invention is operableto process an output from a magnetic sensor array including a pluralityof magnetic sensor elements arranged in an array, and includes aregulating circuit for reducing an offset variation of the output fromthe magnetic sensor elements arranged in the array.

According to this construction, thanks to the regulating circuit, theoffset variation of the outputs from the magnetic sensor elementsarranged in an array can be reduced. For this reason, it is possible toachieve a highly precise detection with minimized offset variation andthe quality of the output signal of the sensor array can be increased.For example, where the magnetic array sensor circuit is applied in, forexample, the rotation detecting apparatus, it is possible to increasethe quality of the output signal from the magnetic sensor array tothereby secure the precision of detection of the rotational angle.

In the magnetic array sensor circuit of the present invention, theregulating circuit referred to above may include a control circuit foroperating the magnetic sensor element in a linear region.

In the case of this construction, by allowing the magnetic sensorelements to operate in the linear region, the offset variation of themagnetic sensor elements can be reduced, and by the utilization of areference sensor so that a reference offset value can counterbalancethem, offsets in the magnetic array sensor circuit and influencesbrought about by change in environment can be removed. In other words,variation of the output signal from the sensor array can be suppressedand undesirable reduction in detecting performance which would otherwisebe brought about by the change in environment can be minimized. Forthose reason, by applying the magnetic array sensor circuit is appliedto, for example, the rotation detecting device, the variation of theoutput signal of the magnetic sensor array can be suppressed to increasethe rotational angle detecting precision and, at the same time,reduction in performance of the rotational angle detection resultingfrom the change in environment can also be minimized.

In the magnetic array sensor circuit of the present invention, themagnetic sensor elements may be employed in the form of a magnetictransistors, each having two drain terminals, in which case the controlcircuit causes the magnetic sensor elements to operate in the linearregion while respective voltages at the two drain terminals of themagnetic sensor element are rendered to be at the same potential. Themagnetic transistor referred to above may be a magnetic transistor of afield effect type (MAGFET). This type of magnetic transistor, when undera condition in which the gate voltage is fixed, the drain voltage islowered to allow the operating condition of the magnetic transistor toshift from that in a saturated region to that in a linear region,results in reduction of the offset variation. In order to realize thisphenomenon, it is necessary to maintain the respective voltages at thetwo drain terminals of the magnetic transistor at the same potential asfar as possible. Accordingly, by the use of the control circuit having afunction of maintaining the drain terminal voltages at the samepotential without relying on the electric current flowing, it ispossible to realize the circuit capable of read out the signal whilesuppressing the offset variation.

The control circuit for rendering the two drain terminal voltages to bethe same potential may be of, for example, a circuit configurationcapable of detecting two drain terminal voltages and performing afeedback so that the two drain terminals can be held at the samepotential. For such control circuit, the control circuit including afull differential amplifier circuit or a single-ended amplifier circuitcan be employed suitably. In either one of the full differentialamplifying circuit and the single-ended amplifier circuit, the drainterminals can be held at the same potential owing to the feedbackreferred to above. Where the control circuit includes the single-endedamplifier circuit, the control circuit may be of a type in which anoffset within the amplifying circuit can be compensated for by an offsetcompensating circuit made up of a switch and a capacitor.

In the magnetic array sensor circuit of the present invention, theregulating circuit referred to above may include a reference sensorelement in the form of the magnetic sensor element short-circuitedbetween two output terminals, a storage element for storing a sensorsignal, read out from the reference sensor element by selecting thelatter, as a reference offset value, and a subtraction circuit forsubtracting the stored reference offset value from an output of theother magnetic sensor elements, whereby an offset and drift of themagnetic array sensor circuit in its entirety are eliminated by thissubtraction.

According to this construction, since the two output terminals of thereference sensor element are short-circuited with each other and, hence,no offset occur, only an offset error generated inside the read-outcircuit comprised of the amplifying circuit or the like can be extractedand appear in the output. This offset error is stored as a referenceoffset value and is subtracted from the output of each of the othermagnetic sensor elements. Accordingly, even though the circuit conditionof the magnetic array sensor circuit and the magnetic sensor elementsforming the magnetic sensor array changes with change of temperature,the offset error of the circuit can be measured each time it occurs sothat the actual sensor signal can be corrected and, therefore, it ispossible to secure the output signal stable enough to be hardly affectedby the environmental influence.

Also, the reference offset value storage element referred to above maybe of a type capable of storing the reference offset value in the formof a ND converted digital value, and the subtraction circuit referred toabove may be of a type capable of performing subtraction from the outputof each of the magnetic sensor element using a digital value. Again, thereference offset value storage element may be a capacitor for storingthe reference offset value in the form of an analog voltage and thesubtraction circuit may be an analog subtraction circuit.

In addition, storage of the offset value may be carried out each time asignal of one line of the sensor array is read out, thereby cancelling adrift of the circuit resulting from change in environment.

In this way, subtraction, that is, cancellation, of the offset error canbe accomplished depending on the circuit condition at the time of eachline read-out and, therefore, the output signal stable enough to behardly affected by the environmental influence can be obtained.

The rotation detecting apparatus according to a third aspect of thepresent invention includes a magnetic sensor array including a pluralityof magnetic sensor elements arranged in an array, a magnet rotatable inface-to-face relation with the magnetic sensor array, and a magneticarray sensor circuit for calculating a rotation angle of the magnetrelative to the magnetic sensor array from an output of the magneticsensor array. The magnetic array sensor circuit referred to above isthat of the present invention.

According to this construction, by operating the magnetic sensorelements forming the magnetic sensor array in the linear region, it ispossible to reduce the offset variation of the magnetic sensor elements.Yet, the influence brought about by the environmental change and theoffset occurring in the magnetic array sensor circuit can also beeliminated. As a result, the angle detecting accuracy of the rotationdetecting device can increase and the resolution and precision as arotary encoder can also increase.

BRIEF DESCRIPTION OF THE DRAWINGS

In any event, the present invention will become more clearly understoodfrom the following description of preferred embodiments thereof, whentaken in conjunction with the accompanying drawings. However, theembodiments and the drawings are given only for the purpose ofillustration and explanation, and are not to be taken as limiting thescope of the present invention in any way whatsoever, which scope is tobe determined by the appended claims. In the accompanying drawings, likereference numerals are used to denote like parts throughout the severalviews, and:

FIG. 1 is a perspective view showing a schematic structure of a rotationdetecting apparatus according to a first preferred embodiment of thepresent invention;

FIG. 2 is a perspective view showing a semiconductor chip used in therotation detecting apparatus according to the first embodiment of thepresent invention;

FIG. 3 is a circuit block diagram showing an electric circuit formed onthe semiconductor chip of the rotation detecting apparatus according tothe first embodiment of the present invention;

FIG. 4 is a plan view showing an example of a group of sensor elementsused to form a magnetic sensor array in the rotation detecting apparatusaccording to the first embodiment of the present invention;

FIG. 5A is a plan view of one of the magnetic sensor elements used inthe rotation detecting apparatus according to the first embodiment ofthe present invention;

FIG. 5B is a sectional view of the magnetic sensor element used in therotation detecting apparatus according to the first embodiment of thepresent invention;

FIG. 5C is a perspective view of the magnetic sensor element used in therotation detecting apparatus according to the first embodiment of thepresent invention;

FIG. 6 is a diagram showing Charts of waveforms of respective outputsfrom the magnetic sensor elements forming the magnetic sensor array;

FIG. 7 is a schematic diagram showing a process of calculating the anglethat is performed by an angle calculating unit;

FIG. 8A is a circuit diagram showing the flow of an electric currentincident to a stress in the combined sensor element group;

FIG. 8B is a circuit showing the flow of the electric current occurringwhen a magnetic field is applied to the combined sensor element group inFIG. 8A;

FIG. 9A is a circuit diagram showing the flow of the electric currentincident to the stress in the combined sensor element group that is usedin a different connection;

FIG. 9B is a circuit showing the flow of the electric current occurringwhen a magnetic field is applied to the combined sensor element groupused in the different connection in FIG. 9A;

FIG. 10 is a circuit diagram showing one example of a connection switch;

FIG. 11A is a circuit diagram showing the flow of the electric currentincident to the stress in the combined sensor element group that is usedin a further connection;

FIG. 11B is a circuit showing the flow of the electric current occurringwhen a magnetic field is applied to the combined sensor element groupused in the further connection in FIG. 11A;

FIG. 12 is a circuit block diagram showing the electric circuit formedon the semiconductor chip of the rotation detecting apparatus accordingto a second preferred embodiment of the present invention;

FIG. 13A is a circuit diagram showing one example of a signal read-outcircuit used in the rotation detecting apparatus according to the secondembodiment of the present invention;

FIG. 13B is a timing chart showing the operation of the signal read-outcircuit according to the second embodiment of the present invention;

FIG. 14A is a circuit diagram showing the operation of the signalread-out circuit during selection of the sensor elements according tothe second embodiment of the present invention;

FIG. 14B is a timing chart showing the operation of the signal read-outcircuit during the selection of the sensor elements according to thesecond embodiment of the present invention;

FIG. 15A is a circuit diagram showing the operation of the signalread-out circuit during signal read-out according to the secondembodiment of the present invention;

FIG. 15B is a timing chart showing the operation of the signal read-outcircuit during the signal read-out according to the second embodiment ofthe present invention;

FIG. 16 is a circuit diagram showing one example of an integratingcircuit used in the signal read-out circuit according to the secondembodiment of the present invention;

FIG. 17A is a circuit diagram showing a modified signal read-out circuitaccording to the second embodiment of the present invention;

FIG. 17B is a timing chart showing the operation of the modified signalread-out circuit according to the second embodiment of the presentinvention;

FIG. 18 is a circuit block diagram showing the circuit formed on thesemiconductor chip used in the rotation detecting apparatus according toa third preferred embodiment of the present invention;

FIG. 19 is a block diagram showing one example of a magnetic arraysensor circuit used in the rotation detecting apparatus shown in FIG.18;

FIG. 20A is a plan view of a magnetic transistor;

FIG. 20B is a circuit diagram showing an electric circuit of themagnetic transistor;

FIG. 21 is a graph showing offset outputs from the magnetic sensorelements used in the magnetic sensor array;

FIG. 22 is a graph showing the relation between a drain voltage and anoffset variation in the magnetic transistor;

FIG. 23 is a circuit diagram showing one example of a control circuitused in the magnetic array sensor circuit;

FIG. 24 is a circuit diagram showing another example of the controlcircuit used in the magnetic array sensor circuit;

FIG. 25 is a circuit block diagram showing the manner in which referencesensor elements are selected in the magnetic array sensor circuitaccording to a fourth preferred embodiment of the present invention;

FIG. 26 is a circuit block diagram showing the manner in which themagnetic sensor elements are selected in the magnetic array sensorcircuit according to the fourth embodiment of the present invention;

FIG. 27 is a circuit block diagram showing the magnetic array sensorcircuit according to a fifth preferred embodiment of the presentinvention;

FIG. 28 is a sectional view showing one example of a rolling bearingassembly equipped with the rotation detecting apparatus of the presentinvention;

FIG. 29 is a longitudinal sectional view showing a conventional bearingassembly;

FIG. 30 is a circuit diagram showing a conventional parallel connectedarrangement of the magnetic sensor elements;

FIG. 31 is a schematic diagram showing the piezoresistive effect actingon a silicon wafer; and

FIG. 32A is schematic diagram showing the piezoresistive effectoccurring in the parallel connected arrangement of the sensor elementsshown in FIG. 29.

FIG. 32B is schematic diagram showing the piezoresistive effectoccurring in the parallel connected arrangement of the sensor elementsshown in FIG. 29.

DESCRIPTION OF THE EMBODIMENTS

A rotation detecting apparatus according to a first preferred embodimentof the present invention will be described with reference to theaccompanying drawings. FIG. 1 illustrates the principle of the rotationdetecting apparatus according to the first embodiment of the presentinvention. A rotatable member 1 and a non-rotatable member 2 represent,respectively, members on rotatable and non-rotatable sides that rotaterelative to each other and, more specifically, the rotatable member 1 isrepresented by a rotating raceway ring of a bearing assembly and thenon-rotatable member 2 is represented by a stationary raceway ring ofthe bearing assembly. This rotation detecting apparatus 3 includes amagnet 4, which forms a magnetic generating element arranged on therotatable member 1, a magnetic sensor array 5 arranged on thenon-rotatable member 2, and an angle calculating unit 6 for calculatingthe rotation angle of the magnet 4 from an output of the magnetic sensorarray 5. The magnetic sensor array 5 is disposed spaced a slightdistance from the magnet 4.

The magnet 4 is of a kind, in which a magnetism emanating therefrom hasan anisotropy in a direction circumferentially about a rotation axis Oof the rotatable member 1, and is in the form of either a permanentmagnet or a complex made up of a permanent magnet and a magneticmaterial. In the illustrated instance, the magnet 4 is of a simple androbust structure including a single permanent magnet 7 sandwiched by andintegrated with two magnetic yokes 8 and 8 to render the assembly torepresent a generally U-shaped configuration, in which one of themagnetic yokes 8 has one end polarized to an N pole and the other of themagnetic yokes 8 has one end polarized to an S pole. This magnet 4 isfitted to the rotatable member 1 with its longitudinal axis aligned withthe rotation axis O of the rotatable member 1 and, accordingly, the Nand S poles turn around the rotation axis O as the rotatable member 1rotates.

The magnetic sensor array 5 is a sensor for detecting the magnetismemanating from the magnet 4 and is arranged on the non-rotatable member2 so as to confront the magnet 4 in a direction along the rotation axisO of the rotatable member 1. As shown in FIG. 2, the magnetic sensorarray 5 is arranged on a single semiconductor chip 9 so as to occupyfour sides of an imaginary square shape, with the center O′ of suchimaginary square shape aligned with the rotation axis O of the rotatablemember 1.

As shown in FIG. 4, a magnetic sensor component forming each of sensortrains 5A to 5D is made up of a combined sensor element group 16including four sensor elements 5 a to 5 d. The four sensor elements 5 ato 5 d of each combined sensor element group 16 are so arranged as to beoriented vertically and horizontally in four directions and areconnected parallel to each other. In such case, of two drain terminalsD1 and D2 of each of the sensor elements 5 a to 5 d, the first drainterminals D1 (represented by the black circle) are connected with eachother and the second drain terminals D2 (represented by the whitecircle) are connected with each other. Each of the sensor trains 5A to5D is made up of a plurality of the combined sensor element groups 16lined up in one direction and each combined sensor element group 16 isregarded and handled as one sensor device in each of the sensor trains5A to 5D.

The semiconductor chip 9, which has a surface mounted with the sensorarray 5 as described above, is fitted to the non-rotatable member 2 withthe sensor-mounted surface confronting the magnet 4. The semiconductorchip 9 referred to above is in the form of a silicon chip.

For each of the magnetic sensor elements 5 a to 5 d, a magnetictransistor of a field effect type (MAGFET) or a Hall element can beused, while the illustrated embodiment will be described in detail withthe magnetic transistors (MAGFETs) employed therein. FIGS. 5A to 5Cillustrate the structure of each of the magnetic sensor elements 5 a to5 d shown in plan, sectional and perspective representations,respectively. Each magnetic sensor element 5 a to 5 d is in the form ofa MAGFET (a magnetic transistor T of a field effect type) and has a gateelectrode 36 positioned, through an oxide layer 35, between a sourceregion 33 and a drain region 34, both of the regions formed on a surfacelayer of a p-Si substrate 32. The drain region 34 is divided into twosegments 34 ₁ and 34 ₂ spaced apart from each other, with the drainterminals D1 and D2 defined in the respective drain segments 34 ₁ and 34₂.

In this magnetic sensor element 5 a to 5 d, since the Lorentz force actson electrons e⁻ flowing from the source region 33 towards the drainregion 34 and the electric currents I, and I₂ flowing in the respectivetwo drain terminals D1 and D2 vary with the intensity of the magneticfield Bz, the intensity of the magnetic field Bz applied to therespective sensor element 5 a to 5 d can be detected.

In a semiconductor circuit formed in a silicon wafer, due to variousfactors involved in the process of manufacturing thereof, the presenceof variation in characteristics of elements is unavoidable. In thesensor element 5 a to 5 d such as shown in FIG. 5, it is ideal that therespective amounts of the drain currents I, and I₂ are equal to eachother in the absence of the magnetic field, but in practice, an offsetsignal appears in small amounts for each element. Where outputs of aplurality of sensor components arranged in an array are used todetermine a distribution of the magnetic field emanating from a magnetarranged in face-to-face relation therewith and the rotational angle iscalculated in reference to the magnetic field distribution, the offsetsignals generated by those components will serve as noise in themagnetic field distribution and will therefore lower the angle detectingaccuracy.

Of those offset signals, the offset signal resulting from stresses inthe sensor chip that causes the reduction of the angle detectingaccuracy can be avoided in a manner as will be described later when thesensor elements 5 a to 5 d oriented vertically and horizontally in fourdirections are connected parallel to each other to define the respectivecombined sensor element group 16.

The angle calculating unit 6 shown in FIG. 1 is in the form of anintegrated circuit and is, as shown in FIG. 2, mounted on thesemiconductor chip 9 together with the magnetic sensor array 5. Thisangle calculating unit 6 is arranged inside the square shape depicted bythe magnetic sensor array 5. Accordingly, it is possible to arrange themagnetic sensor array 6 and the angle calculating unit 6 compactly.

FIG. 3 illustrates a schematic structure of a circuit on thesemiconductor chip 9 that is applicable where the angle calculating unit6 is so designed as to provide an absolute output. In addition to thearrangement of the combined sensor element groups 16, each of the sensortrains 5A to 5D includes an amplifier 11 for amplifying an output fromthe respective sensor train 5A to 5D. Also, an A/D converter 12 forconverting an analog output, which has been amplified by thecorresponding amplifier 11, into a digital output is connected betweeneach sensor train 5A to 5D and the angle calculating unit 6. The anglecalculating unit 6 includes a spatial filter 13 for removing noises fromthe digital output of the ND converter 12, a zero detector 14 fordetecting a zero-crossing in the magnetic field distribution from anoutput of the spatial filter 13 and an angle calculator 15 forcalculating the rotation angle of the magnet 4 from an output of thezero detector 14. The spatial filter 13 referred to above has a functionof reducing noises resulting from variation in sensors by digitallyfiltering the output from the magnetic sensor array 5 and may beemployed in the form of a comb filter.

FIGS. 6 and 7 show respective explanatory diagrams used to explain theangle calculating process performed by the angle calculator 15. Inparticular, Charts (A) to (D) in FIG. 6 show waveforms of respectiveoutputs from the magnetic sensor trains 5A to 5D forming the magneticsensor array 5, which are generated during rotation of the rotatablemember 1, in which the axis of abscissas represents each combined sensorelement group 16 of each of the sensor trains 5A to 5D and the axis ofordinates represents the intensity of the detected magnetic field.

Let it be assumed that the zero-crossing positions, which indicate aboundary between the N and S poles of the magnetic field, detected bythe magnetic sensor array 5 lie at respective positions X1 and X2 shownin FIG. 7. In this condition, outputs from the sensor trains 5A to 5D ofthe magnetic sensor array 5 represent such signal waveforms as shown inCharts (A) to (D), respectively. Accordingly, the zero-crossingpositions X1 and X2 can be calculated from the respective outputs of thesensor trains 5A and 5C by means of collinear approximation.

Calculation of the angle can be carried out by use of the followingequation (1):θ=tan⁻¹(2L/b)  (1)wherein θ represents the value of the rotation angle θ of the magnet 4expressed in terms of the absolute angle; 2L represents the length ofeach of the four sides of the magnetic sensor array 5 made up of thesensor trains 5A to 5D arranged in the square pattern; and b representsthe transverse length between the zero-crossing positions X1 and X2.

If the zero-crossing positions X1 and X2 lie in the sensor trains 5B and5D, the rotation angle θ can be calculated in a manner similar to thatdescribed above, based on data on the zero-crossing positions obtainedfrom the respective outputs of those sensor trains 5B and 5D.

The magnetic sensor elements 5 a to 5 d forming each of the combinedsensor element groups 16 in the magnetic sensor array 5 are connectedparallel to each other in the manner shown in and described withreference to FIG. 4. Because of this, it is possible to reduce theinfluence brought about by the stress, where the stress acts on thesemiconductor chip 9 in a direction shown by the arrow S in FIG. 8A,accompanied by an imbalance in resistivity. In other words, since thefour sensor elements 5 a to 5 d are so arranged as to be orientedvertically and horizontally in four directions, the sensor elements 5 ato 5 d are so oriented as to be displaced 90° from each other. In thosesensor elements 5 a to 5 d so displaced 90° from each other, the effectsof stresses are reversed. As such, by arranging the four sensor elements5 a to 5 d forming each of the combined sensor element groups 16 in themagnetic sensor array 5 so as to be oriented vertically and horizontallyin four directions and by connecting parallel to each other to therebyform the respective combined sensor element group 16 as hereinbeforedescribed, the respective offset signals of the sensor elements 5 a to 5d resulting from the warp occurring in the semiconductor chip 9 can bereduced in the magnetic signal outputted from the magnetic sensor array5.

When during the condition shown in FIG. 8A, the magnetic field Bz isfurther applied as shown in FIG. 8B, magnetic filed signals from thesensor elements 5 a to 5 d are summed together, but the offset signalsresulting from the stresses are counterbalanced with each other and,accordingly, the offset signals can be reduced in a sensor signaloutputted from the combined sensor element group 16.

Also, where in the four magnetic sensor elements 5 a to 5 forming therespective combined sensor element group 16, the mode of connection isreversed as shown in FIG. 9 to that described hereinabove, the magneticfield signals are counterbalanced and only the offset signals resultingfrom the stresses will be outputted. The mode of connection shown inFIG. 9 is such that the first drain terminals D1 of two of the magneticsensor elements 5 a and 5 b placed in the vertical direction and thesecond drain terminals D2 of the remaining sensor elements 5 c and 5 dplaced in the transverse direction are connected together. In the caseof the mode of connection shown in FIG. 9, the stress signal will beoutputted from the combined sensor element group 16, allowing themagnetic sensor array 5 to function as a stress sensor.

It is to be noted that the semiconductor chip 9 may be provided thereonwith an additional circuit, which serves as a connection mode selectingunit 19A for selecting one of the mode of connection shown in FIG. 8 andthe mode of connection shown in FIG. 9, so that the only magnetic sensorarray 5 can be selectively used as a rotation sensor or a stress sensor.Selection of one of those modes of connection is preferably accomplishedin response to a predetermined signal supplied from an external part.

FIG. 10 illustrates one example of the circuit that serves as theconnection mode selecting unit 19A, which includes two selectingswitches 71 and 72 operable in response to an external switching signalto change connections of wirings 73 ₁ to 73 ₄ which are used to connectbetween the magnetic sensor elements 5 a to 5 d. Each of the selectingswitches 71 and 72 is employed in the form of a semiconductor switchingelement.

In addition, for the magnetic sensor array 5, the magnetic sensor array5 including the combined sensor element groups 16 connected in the modeshown in FIG. 8 and the magnetic sensor array 5 including the combinedsensor element groups 16 connected in the mode shown in FIG. 9 may be sojuxtaposed relative to each other that only one of respective outputsfrom the magnetic sensor arrays 5 can be selected. Even in this way, therotation sensor and the stress sensor can be selectively utilized one ata time.

As described above, according to the rotation detecting apparatus 3 ofthe structure described hereinabove, since the sensor elements of themagnetic sensor array 5 are formed as the combined sensor element groups16 each including the four sensor elements and since the four sensorelements 5 a to 5 d forming each combined sensor element group 16 are soarranged as to be oriented vertically and horizontally in fourdirections and are connected parallel to each other, it is possible toreduce in the magnetic signal outputted from the magnetic sensor array5, the offset signals of the sensor elements 5 a to 5 d resulting fromthe stress occurring in the silicon chip. As a result thereof, the angledetecting precision of the rotation detecting apparatus 3 increases andthe resolution and the precision as a rotary encoder can be improvedaccordingly.

Also, as measures to reduce the offset signals, no change is required inthe process of manufacturing of the sensor elements 5 a to 5 d and,accordingly, the cost will not be increased.

Yet, since in this first embodiment, the four sensor elements 5 a to 5 dof each combined sensor element group 16 are arranged in a cruciformpattern, the wirings necessary to connect between the sensor elements 5a to 5 d are small in length and can therefore be simplified.

It is to be noted that although in the foregoing embodiment, the foursensor elements 5 a to 5 d forming each of the combined sensor elementgroups 16 has been shown and described as arranged in a cruciformpattern, the pattern of arrangement of the four magnetic sensor elements5 a to 5 d may not be always limited to the cruciform pattern as long asthe same mode of connection is employed. By way of example, as shown inFIGS. 11A and 11B, the two sensor elements 5 c and 5 d, which are laidtransverse, may be juxtaposed in a vertical direction relative to theother two sensor elements 5 a and 5 b juxtaposed in the verticaldirection. FIG. 11A illustrates a condition under stress and FIG. 11Billustrates a condition in which under the stress the magnetic field Bzis applied. Connection between the sensor elements 5 a to 5 d are notshown for the sake of brevity.

As hereinabove described, where the four sensor elements 5 a to 5 d ofeach combined sensor element group 16 are arranged dispersed, the sensorelements 5 a to 5 d are flexibly arranged, therefore, it is possible toefficiently arrange the sensor elements 5 a to 5 d with unnecessaryregions being minimized in the substrate.

FIG. 12 is a circuit block diagram showing the circuit formed in thesemiconductor chip used in the rotation detecting apparatus according toa second preferred embodiment of the present invention.

The difference between this second embodiment and the first embodimentshown in FIG. 3 lies in that in place of the amplifier 11 employed inthe first embodiment, a sensor signal read-out circuit 60 is employed.Magnetic sensor components 50 forming each of the sensor trains 5A to 5Don the four sides are of a structure identical with those shown in anddescribed with particular reference to FIG. 5.

FIG. 13A illustrates an example of a circuit arrangement of the sensorsignal read-out circuit 60. This sensor signal read-out circuit 60includes a power supply circuit 80 and a current integrating circuit 81and is operable to select the magnetic sensor elements (MAGFETs) 50forming the magnetic sensor array 5 sequentially according to the orderof arrangement thereof, to convert output currents thereof intocorresponding voltage and finally to read out them.

The power supply circuit 80 is of a switched-current system. This powersupply circuit 80 includes a series connected circuit section 82including series-connected transistors Q1 and Q2 and connected at oneend with an electric power source terminal and at the other end with aread-out line loP, as well as a series connected circuit section 83including series-connected transistors Q3 and Q4 and connected at oneend with the electric power source terminal and at the other end withthe other read-out line loM. Respective gates of the transistors Q1 andQ3 are connected with the electric power source terminal through a biassupply capacitor Cm for bias supply and those gates and the read-outlines loP and loM are connected together through switches MEM and RST.The read-out line loP and loM referred to above are in turn connectedwith each of the magnetic sensor elements (MAGFETs) 50 throughcorresponding selector switching transistors SEL-SW.

The electric current integrating circuit 81 is in the form of a fulldifferential amplifier circuit including an OP amplifier 84, capacitorsC, and switches RST and has two input terminals connected respectivelywith the read-out lines loP and loM through switches SAM.

Hereinafter, the operation of the sensor signal read-out circuit 60 willbe described. The various switches employed therein operate atrespective timings shown in the timing chart in FIG. 13B. It is to benoted that in this timing chart shown in FIG. 13B, each switch is shownas triggered on when the signal is in a high level state H.

At the outset, a select signal SEL for selecting one of the magneticsensor elements 50 is held in a high level state H. Then the switchesMEM and RST are triggered on. The circuit under this condition is shownin FIG. 14A. The selected magnetic sensor element 50 is held by anapplied bias voltage Vbs in a condition ready to flow a predeterminedelectric current and, in the illustrated instance, in a condition inwhich the sum of the electric currents at the two drain terminals is2lo. When the magnetic field is applied to the magnetic sensor element50, the imbalance occurs between the two drain terminal currents andelectric currents lo+Δl and lo−Δl flow through the read-out lines loPand loM, respectively.

On the other hand, since the switches MEM and RST in the power supplycircuit 80 are turned on, the read-out lines loP and loM areshort-circuited. Also, since the respective gates of the transistors Q1and Q3 are connected with the read-out lines loP and loM, the powersupply circuit 80 is diode-connected to supply the sum 210 of thecurrents flowing through the magnetic sensor elements 50. In otherwords, respective gate terminal voltages Vg of the transistors Q1 and Q3become equal to potentials at the read-out lines loP and loM with anelectric current lo flowing through the left and right series connectedcircuit sections 82 and 83. In the electric current integrating circuit81, since the switch SAM is turned off, it is isolated from the powersupply circuit 80 and opposite ends of the capacitor C areshort-circuited through the switch RST, thereby holding a resetcondition.

Important to note during this condition is that the capacitor Cm isconnected to the respective gate terminals of the transistors Q1 and Q3of the power supply circuit 80 with the gate voltage Vg stored therein.Even when starting from this condition the switch MEM is turned off, thestate of the power supply circuit 80 is maintained by the voltage Vgstored in the capacitor Cm and, therefore, the electric current locontinues to flow through the left and right series connected circuitsections 82 and 83.

By turning on the switch SAM at this time, the electric currentintegrating circuit 81 is connected with the read-out lines loP and loM,and when the switch RST is subsequently turned off, a conditionestablishes in which the differential current is accumulated in thecapacitor C. This condition is shown in FIG. 15A. As hereinabovedescribed, although the power supply circuit 80 operated in a conditionto supply the electric current lo to the left and right series connectedcircuit sections 82 and 83, differences +Δl and −Δl therebetween aresupplied to the electric current integrating circuit 81 since electriccurrents flowing through the magnetic sensor elements are lo+Δl andlo−Δl. The electric current integrating circuit 81 starts theaccumulating operation thereof when and after the switch RST is turnedoff and terminates it when the switch SAM is turned off. By controllingthe length of time Δt during which charging takes place, the voltageVout outputted can be controlled.

In other words, by carrying out the integration for a period of Δt, avoltage expressed by the following equation (2) can be generated:Vout=2×Δt×Δl/C  (2)

When the minute differential current Δl is 1 μA, the voltage Vout of 1volt is obtained by setting the capacitor C to 1 pF and Δt to 0.5 μs. Itis to be noted that in FIG. 13A, the current integrating circuit 81 isshown as employed in the form of the full differential amplifiercircuit, but it may alternatively have a circuit configuration operableto merely charge on the capacitor C as shown in FIG. 16.

As described above, since in the rotation detecting apparatus 3according to this embodiment, the provision is made of the sensor signalread-out circuit 60 operable to sequentially select the plural magneticsensor elements 50 forming the magnetic sensor array 5, to extract asignal component from the flowing electric current and to read out itafter having been converted into the voltage, the electric current to besupplied to the magnetic sensor elements 50 may be of an amount requiredby one component. For this reason, the detection signal can be read outwhile the current consumption is minimized.

In this embodiment, since the power supply circuit 80 of the sensorsignal read-out circuit 60 is chosen to be of the switched-currentsystem, a change of the minute sensor current caused by externalmagnetic field can be extracted purely in the form of a differentialcurrent component. Also, since the extracted differential currentcomponent is converted into an electric voltage signal by means of theelectric current integrating circuit 81 utilizing the capacitor C toperform charging for a predetermined length of time, the voltage signalof a sufficient amplitude necessary for the A/D conversion and thesignal processing in the subsequent stage can be obtained. In addition,by properly setting the capacitance of the capacitor of the currentintegrating circuit 81, it is possible to achieve the conversion intothe large voltage signal in an extremely short time of charging and toconstruct the sensor signal read-out circuit 60 having a high speed anda sufficient amplification factor.

A different example of the circuit construction of the sensor signalread-out circuit 60 referred to above is shown in FIG. 17A. In thissensor signal read-out circuit 60A, the details of connection betweenthe magnetic sensor elements 50 and the read-out lines loP and loM andthe details of the current integrating circuit 81 are substantiallyidentical with those shown in and described with particular reference toFIG. 13A. However, the sensor signal read-out circuit 60A shown in FIG.17A differs from that shown in FIG. 13A in that the power supply circuit80A employed therein is of a current mirror type. In other words, thepower supply circuit 80A of the sensor signal read-out circuit 60A shownin FIG. 17A includes a first circuit section 85, connected with theread-out line loP, and a second circuit section 86 connected with theread-out line loM.

The first circuit section 85 includes a diode-connected pMOS circuit 87including transistors Q11 and Q12 interposed between the electric powersource terminal and the read-out line loP, and current mirror circuits89A, 89B, 90A and 90B. The current mirror circuit 89A and 89Brespectively include transistors Q13, Q14 and transistors Q15, Q16having their gates connected with respective gates of the transistorsQ11, Q12 of the pMOS circuit 87 and are connected at one end with theelectric power source terminals. The current mirror circuits 90A and 90Bare of an nMOS circuit construction including transistors Q17, Q18 andtransistors Q19, Q20 interposed between the opposite ends of the currentmirror circuits 89A and 89B and the ground terminals, respectively.

The second circuit section 86 includes a diode-connected pMOS circuit 88including transistors Q21 and Q22 interposed between the electric powersource terminals and the read-out line loM, and current mirror circuits91A, 91B, 92A and 92B. The current mirror circuit 91A and 91Brespectively include transistors Q23, Q24 and transistors Q25, Q26having their gates connected with respective gates of the transistorsQ21 and Q22 and connected at one end with the electric power sourceterminals. The current mirror circuits 92A and 92B are of an nMOScircuit construction including transistors Q27, Q28 and transistors Q29,Q30 interposed between the opposite ends of the current mirror circuits91A and 91B and the ground terminals, respectively.

The current mirror circuit 89B is connected at the opposite end with theopposite end of the current mirror circuit 92B, and the current mirrorcircuit 90B is connected at the opposite end with the opposite end ofthe current mirror circuit 91B. The opposite ends of the current mirrorcircuits 91B and 92B are each connected with the electric currentintegrating circuit 81 through the switch SAM. The various switchesemployed in this circuit operate at respective timings shown in thetiming chart of FIG. 17B.

In the above described circuit, the pMOS circuits 87 and 88 are held ina condition to supply an electric current flowing towards the magneticsensor element 50 that has been selected and are operable to supply theelectric currents lo+Δl and lo−Δl, respectively. The current mirrorcircuits 89A, 89B and 91A, 91B respectively connected with thosecircuits 23 and 24 serve as current source circuits capable ofgenerating the same electric currents as those flowing towards the pMOScircuits 87 and 88. Similarly, the current mirror circuits 90A, 90B, 92Aand 92B connected with the current mirror circuits 89A, 89B, 91A and 91Bserve as current source circuits capable of generating the same electriccurrents. The current integrating circuit 81 is supplied with +2Δl fromthe opposite end of the current mirror circuit 92B and with −2Δl fromthe opposite end of the current mirror circuit 91B.

In the current integrating circuit 81, the switches are operated in amanner as shown in the timing chart of FIG. 17B. When the switch RST isturned off while the switch SAM is turned on, the current integratingcircuit 81 starts the integrating operation thereof, which continuestill the time the switch SAM is turned off. As is the case with thecircuit shown in FIG. 13A, by carrying out the integration for a periodof Δt, a voltage Vout is generated. In such case, when Δl is 1 μA, thevoltage of Vout=2 volt can be obtained by setting the capacitor C to 1pF and Δt to 0.5 μs.

Even in this sensor signal read-out circuit 60A, although the currentintegrating circuit 81 has been shown and described as employed in theform of the full differential amplifier circuit, it may be of a circuitconfiguration operable to merely charge on the capacitor C as shown inFIG. 16.

As hereinabove described, even when the power supply circuit 80A in thesensor signal read-out circuit 60A is of the current mirror system, achange of the minute sensor current caused by external magnetic fieldcan be extracted purely in the form of a differential current component.

Hereinafter, an embodiment of the magnetic array sensor circuit and therotation detecting apparatus utilizing this magnetic array sensorcircuit according to the present invention will be described withparticular reference to the accompanying drawings.

FIG. 18 is a circuit block diagram showing the circuit configuration ofthe semiconductor chip employed in the rotation detecting apparatusaccording to a third preferred embodiment of the present invention andparticularly shows the circuit configuration of the semiconductor chip 9applicable where an absolute output is obtained from the anglecalculating unit 6. This third embodiment differs from the firstembodiment shown in and described with particular reference to FIG. 3 inthat in place of the amplifier 11 employed in the first embodiment, amagnetic array sensor circuit 61 is employed.

As shown therein, each sensor train 5A to 5D (FIG. 2) on each side ofthe square shape is comprised of the magnetic sensor elements 5 ₁ to 5_(n) and the magnetic array sensor circuit 61 of the present inventionhaving a read-out section. The magnetic sensor elements 5 ₁ to 5 _(n)are employed in the form of, for example, a magnetic transistor (MAGFET)and are of the same structure as that shown in and described withreference to FIG. 5. Also, the ND converter 12 for digitalizing ananalog signal outputted from the magnetic array sensor circuit 61 isdisposed between each sensor train 5A to 5D and the angle calculatingunit 6. The angle calculating unit 6 referred to above is of the samecircuit configuration as that shown in and described in connection withthe first embodiment and, accordingly, the details thereof are notreiterated for the sake of brevity.

This magnetic array sensor circuit 61 is of a circuit configurationoperable to process an output from the magnetic sensor array 5, in whichthe magnetic sensor elements 5 ₁ to 5 _(n) are arrayed as shown in FIG.19 (the third embodiment), and includes, in addition to a differentialcurrent detecting circuit 93 and a current-to-voltage converting circuit94, a control circuit 18, which operates the magnetic sensor elements 5₁ to 5 _(n) in a linear region operation, as a regulating circuit forreducing offset variation of an output of the arrayed magnetic sensorarray 5. The magnetic sensor elements 5 ₁ to 5 _(n) are adapted to beselected by a sensor selecting unit 19B sequentially according to theorder of arrangement into operation.

In FIG. 19, there is shown the case in which the currents lo−Δl andlo+Δl respectively flow through the two drain terminals D1 and D2.

The differential current detecting circuit 93 is a circuit operable toextract the difference 2Δl between the two electric currents appearingat the magnetic sensor elements 5 ₁ to 5 _(n). The current-to-voltageconverting circuit 94 is a circuit operable to convert the differentialcurrent, extracted by the differential current detecting circuit 93,into a voltage signal V_(out) to thereby provide a sensor signal.

As described above, by the operation of the differential currentdetecting circuit 93 and the current-to-voltage converting circuit 94,the differential current can be extracted in the presence of themagnetic field applied to the magnetic sensor elements 5 ₁ to 5 _(n) andamplified to the voltage signal, whereby the sensor signal can beobtained in the form of a voltage signal.

The magnetic transistor T forming each of the magnetic sensor elementsis expressed by an equivalent circuit shown in FIG. 20B, and thedifference between currents I₁ and I₂ flowing respectively to the twodrain terminals D1 and D2 provides a magnetic field signalrepresentative of the intensity of the magnetic field Bz. FIG. 20A is aplan view of the magnetic transistor T.

When the magnetic sensor elements 5 ₁ to 5 _(n) each in the form of themagnetic transistor T described above are arranged as illustrated inFIG. 19 to form the magnetic sensor array 5, the sensor outputs willvary with variation in characteristics of the individual elements, whichin turn lead to offset variations.

FIG. 21 illustrates an example of the sensor output signals (offsetsignals) of the magnetic sensor elements 5 ₁ to 5 _(n) in the magneticsensor array 5 in the absence of the magnetic field. When the magneticfield Bz is applied to this magnetic sensor array 5, the output signalchanges, but this output signal is superimposed with the offset signaland, accordingly, it will constitute an obstruction to measurement ofthe distribution of the magnetic field that is dealt with by themagnetic sensor array 5.

According to experiments, by measuring the output of the magnetictransistor is measured, it has been ascertained that depending on theoperating condition of the transistor, the magnitude of an offsetvariation changes. More specifically, in the equivalent circuit diagramshown in FIG. 20B, under conditions where the voltage to be applied tothe gate G of the transistor is fixed to Vg and the voltages at thedrain terminals D1 and D2 are variable as represented by Vd, therelation between Vd and the offset variation represents such as shown inthe chart of FIG. 22. In other words, by lowering the drain voltage Vdto shift the operating condition of the transistor from the operation ina saturation region to the operation in a linear region, the offsetvariation gradually decreases while the gate voltage Vg is fixed.

It may be convenient if by the utilization of this phenomenon, theoffset variation is minimized and the sensor signal can be read out.However, in order to realize this condition, it is necessary to maintainthe voltages Vd at the respective drain terminals D1 and D2 of themagnetic transistors T at the same potential without relying on theflowing current.

The control circuit 18 shown in FIG. 19 performs the function ofmaintaining the voltages Vd at the same potential and, thanks to this,this magnetic array sensor circuit 61 is so operable as to read out thesensor signal while the offset variation is suppressed.

FIG. 23 illustrates one example of the control circuit 18. This controlcircuit 18 is a circuit operable to detect terminal voltages at the twodrain terminals D1 and D2 and maintain them at the same potential. Morespecifically, this control circuit 18 is configured as a feedbackcircuit including transistors Tr1 and Tr2 associated with the respectivetwo drain terminals D1 and D2 (FIG. 20A) and a full differentialamplifier circuit 95. In this control circuit 18, drain terminalvoltages Vd1 and Vd2 are detected and those drain voltages are socontrolled as to be at the same potential (Vd1=Vd2).

FIG. 24 illustrates an example in which for the control circuit 18,single-ended amplifier circuits and capacitors are utilized. The controlcircuit 18 shown therein is in the form of a feedback circuit, eachincluding transistors Tr1 and Tr2 associated with the respective twodrain terminals D1 and D2 (FIG. 20A), single-ended amplifier circuit 96,capacitors C and two switches S1 and S2, and is so designed as to allowthe capacitor to eliminate or compensate an offset of the amplifiercircuit 96. Since this circuit is so structured, on each side of the twodrain terminals D1 and D2, as to cancel the offset of the amplifiercircuit 96 with the capacitor C, the drain terminal voltages Vd1 and Vd2can be controlled to become equal to a reference voltage Vd with highprecision.

The switches S1 and S2 employed in this control circuit 18 are operatedin the following manner:

(1) The switch S1 is kept turned on until the sensor current stabilizes.

(2) Then, the difference Vos between the reference voltage Vd and theactual drain terminal voltages Vd1 or Vd2 is stored in the capacitor C.

(3) At this time, a voltage Vd+Vos is inputted to a feedback terminal(-terminal).

(4) Thereafter, the switch S1 is turned off.

(5) When the switch S2 is subsequently turned on, since the capacitor Cstoring Vos therein is connected with the feedback terminal (-terminal),the voltage at the drain terminal of the sensor becomes Vd and therebythe offset is cancelled.

In this way, the drain terminal voltages Vd1 and Vd2 can be controlledto become equal to the reference voltage Vd with high precision.

As hereinabove described, in the magnetic array sensor circuit 61 shownin FIG. 19, since the drain terminal voltages of the magnetictransistors T, which are the magnetic sensor elements 5 ₁ to 5 _(n), arecontrolled by the control circuit 18 so that the magnetic transistors Tcan be operated in the linear region, it is possible to reduce theoffset variation of the plural magnetic sensor elements 5 ₁ to 5 _(n).For this reason, where the magnetic array sensor circuit 61 is appliedin, for example, the rotation detecting apparatus, it is possible toincrease the quality of the output signal from the magnetic sensor array5 to thereby secure the precision of detection of the rotational angle.

FIGS. 25 and 26 illustrate a fourth preferred embodiment of the presentinvention and are circuit block diagrams showing a condition ofselection of the reference sensor element used in the magnetic arraysensor circuit 61. The magnetic array sensor circuit 61 is similar tothat employed in the practice of the third embodiment shown in FIG. 19,but differ therefrom in that in place of the use of the control circuit(regulating circuit) 18 for operating the magnetic sensor elements 5 ₁to 5 _(n) in the linear region, the use is made of a regulating circuit18A including the reference sensor element 5ref. FIG. 25 illustrates acondition in which the sensor selecting unit 19B selects the referencesensor element 5ref and FIG. 26 illustrates a condition in which thesensor selecting unit 19B selects one of the other magnetic sensorelements 5 ₁ to 5 _(n) (for example, the magnetic sensor element 5 ₁ sofar shown therein).

The regulating circuit 18A of the magnetic array sensor circuit 61includes the reference sensor element 5ref short-circuited with the twooutput terminals (drain terminals) of the magnetic sensor element, anoffset output storage element 97 for storing, as a reference offsetvalue, a sensor signal read out by selecting the reference sensorelement 5ref, and an analog subtraction circuit 98 (FIG. 26) forsubtracting the stored reference offset value from outputs of the othermagnetic sensor elements 5 ₁ to 5 _(n). The offset output storageelement 97 may be an analog element such as a capacitor or may be anelement capable of storing a digital value obtained by A/D converting anoffset error. Also, in place of the analog subtraction circuit 98, acircuit for carrying out the subtraction using digital values may beemployed.

In the meantime, in the standard magnetic array sensor circuit that isemployed in the rotation detecting apparatus, since the magnetic sensorelements such as, for example, Hall elements or magnetic transistorsforming the magnetic sensor array and the signal read-out circuit areformed in the silicon chip, the characteristic may change with change inenvironment such as, for example, temperature and/or warp. When thesignal read out from the magnetic sensor array changes with thisenvironmental change, the final result of detection of the rotationalangle will be adversely affected.

The magnetic array sensor circuit 61 in this fourth embodiment is of atype provided with the reference sensor element 5ref, the offset outputstorage element 97 and the analog subtraction circuit 98 for the sake ofprotecting the rotation detecting apparatus from being easily affectedby such environmental change as discussed above.

The reference sensor element 5ref is, as a part of the magnetic sensorarray 5, arranged together with the magnetic sensor elements 5 ₁ to 5_(n) and can be selected by the sensor selecting unit 19B for operation.Other structural features are substantially similar to that employed inthe embodiment shown in and described with reference to FIG. 19.

In this magnetic array sensor circuit 61, the output signal is processedin the following manner:

(1) As shown in FIG. 25, when the sensor selecting unit 19B selects thereference sensor element 5ref and read out the sensor signal of thereference sensor element 5ref, since the reference sensor element 5refhas two output terminals short-circuited together and is therefore freefrom any offset, only the offset error generated inside the magneticarray sensor circuit 61 comprised of an amplifier circuit and others canbe extracted and appears in an output. In other words, the error of thedifferential current detecting circuit 93 is outputted as loffset, thevalue of which is converted into a voltage by the current-to-voltageconverting circuit 94, such voltage being then outputted as Voffset.

(2) This offset error (the offset voltage Voffset) is stored in theoffset output storage element 97 and an offset error component issubtracted from the actual output signals of the magnetic sensorelements 5 ₁ to 5 _(n) by the analog subtraction circuit 98 as shown inFIG. 26. Specifically, the electric current of the magnetic sensorelement 5 ₁ then selected in FIG. 26 is held out of equilibrium by themagnetic field and becomes currents lo−Δl and lo+Δl, the difference ofwhich is detected by the differential current detecting circuit 93. Thedifferential current so detected is superimposed with an offset of thedifferential current detecting circuit 93 and 2Δl+Ioffset is thereforeoutputted. When this is converted into a voltage by thecurrent-to-voltage converting circuit 94, the offset error Voffsetstored in the offset output storage element 97 is subtracted by theanalog subtraction circuit 98 and, therefore, the offset component canbe cancelled and only the signal component Vout of the outputs of themagnetic sensor elements can be extracted. In this way, the offset errorin the magnetic array sensor circuit 61 can be cancelled.

In the operation described above, storage of the offset error is carriedout at the initial stage of reading one line of the magnetic sensorarray 5. In other words, arrangement may be made that storage of theoffset value is carried out each time signals are read out from one lineof the sensor array to thereby eliminate a drift of the circuitresulting from change in environment. In this way, it is possible tosubtract, that is, cancel the offset error according to the condition ofthe circuits during each line read-out operation and the output signalstable enough to be not easily affected by the change in environment canbe obtained. It is to be noted that the reference sensor element 5refmay be arranged at the front of one line of the magnetic sensor array 5or at the end of one line of the magnetic sensor array 5.

As hereinabove described, in the magnetic array sensor circuit 61according to each of the third and fourth embodiments, even though thecircuit condition of the magnetic sensor elements 5 ₁ to 5 _(n), formingthe magnetic sensor array 5, and the magnetic array sensor circuit 61may change with change in temperature, the offset error of the circuitoccurring that time is measured so that the actual sensor signal can becorrected. Accordingly, the output signal stable enough to be not easilyaffected by the influence brought about by the environment can beobtained.

FIG. 27 illustrates a fifth preferred embodiment of the presentinvention. This fifth embodiment is substantially similar to the fourthembodiment shown in and described with reference to FIGS. 25 and 26, butdiffers therefrom in that in the magnetic array sensor circuit 61employed in the fourth embodiment, the control circuit 18 of the typeemployed in the third embodiment shown in and described with referenceto FIG. 19 is additionally employed.

In the case of this magnetic array sensor circuit 61, not only can theoffset variation of the magnetic sensor elements 51 to 5 n be reducedsufficiently because of the function of the control circuit 18, but theinfluence brought about by the change in environment and offsetoccurring in the magnetic array sensor circuit 61 can also be eliminatedbecause of the functions of the reference sensor elements 5ref, theoffset output storage element 97 and the analog subtraction circuit 98.Accordingly, by employing this magnetic array sensor circuit 61 isemployed in, for example, the rotation detecting apparatus, not only canvariation of the output signal from the magnetic sensor array 5 besuppressed to increase the precision of detection of the rotationalangle, but reduction of the rotational angle detecting performance,which would otherwise result from the change in environment, can also beminimized.

The rotation detecting apparatus utilizing the magnetic array sensorcircuit 61 according to any one of the third to fifth embodiments of thepresent invention is basically similar to the rotation detectingapparatus shown in and described in connection with any one of the firstand second embodiments with reference to FIGS. 1 and 2 and, therefore,the details are not reiterated for the sake of brevity.

According to this rotation detecting apparatus 3, since the magneticarray sensor circuit 61 is employed, it is possible to reduce the offsetvariation of the magnetic sensor elements 5 ₁ to 5 _(n) by operating themagnetic sensor elements 5 ₁ to 5 _(n) forming the magnetic sensor array5 in the linear region. It is also possible to remove the influencebrought about by the environmental change and the offset occurring inthe magnetic array sensor circuit. As a result, the angle detectingprecision of the rotation detecting apparatus 3 increases and theresolution and precision as the rotary encoder increase.

FIG. 28 illustrates a rolling bearing assembly, in which the rotationdetecting apparatus 3 constructed in accordance with any one of theforegoing embodiments is incorporated. It is to be noted thatincorporation of the rotation detecting apparatus 3 in the rollingbearing assembly is equally applicable to any one of the first to fifthembodiment described hereinbefore.

The illustrated rolling bearing assembly 20 is of a type, in which a rowof rolling elements 24, retained by a retainer 23, are interposedbetween respective raceways defined in inner and outer rings 21 and 22.The rolling elements 24 are in the form of a ball and this rollingbearing assembly 20 is so designed as to be a deep groove ball bearing.Also, a sealing member 25 covering one end of a bearing space is fittedto the outer ring 22. The inner ring 21 adapted to be mounted on arotary shaft 10 is supported by the outer ring through the row of therolling elements 24. The outer ring 22 is arranged in a housing of amachine or equipment that utilizes the bearing assembly.

The inner ring 21 has a magnet fitting member 26 fitted thereto, and themagnet 4 is secured to this magnet fitting member 26. The magnet fittingmember 26 is so fitted to the inner ring 21 as to cover one end of abore thereof. More specifically, the magnet fitting member 26 has acylindrical portion 26 a formed in an outer peripheral edge portionthereof, which is mounted on a shoulder outer peripheral surface of theinner ring 21, and a side plate portion in the vicinity of thecylindrical portion 26 a for engagement with an end face of the innerring 21 to allow it to be positioned relative to the axial direction.

The outer ring 22 is fitted with a sensor fitting member 27, to whichthe semiconductor chip 9, shown in FIG. 1, mounted with the magneticsensor array 5 and the angle calculating unit 6, is fixed. Also, anoutput cable 29 for drawing the output externally from the anglecalculating unit 6 is secured to this sensor fitting member 27. Thissensor fitting member 27 is axially positioned, wherefor a free endcylindrical portion 27 a in an outer peripheral portion thereof ismounted on an inner diametric surface of the outer ring 22 with a collar27 b formed in the vicinity of this free end cylindrical portion 27 abeing engaged with an end face of the outer ring 22.

As described above, when the rotation detecting apparatus 3 according toany one of the previously described embodiments is integrated with therolling bearing assembly 20, not only can the number of component partsof the machine or equipment that utilizes the bearing assembly and thenumber of manufacturing steps be reduced, but also compactization can beachieved. In such case, since the rotation detecting apparatus 3 iscompact in size and can provide the rotation angle output with highprecision, a satisfactory rotation angle output can be obtained even ina small sized bearing assembly such as, for example, a small diameterbearing.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings which are used only for the purpose ofillustration, those skilled in the art will readily conceive numerouschanges and modifications within the framework of obviousness upon thereading of the specification herein presented of the present invention.Accordingly, such changes and modifications are, unless they depart fromthe scope of the present invention as delivered from the claims annexedhereto, to be construed as included therein.

1. A magnetic array sensor circuit to process an output from a magneticsensor array including a plurality of magnetic sensor elements arrangedin an array to detect a magnetic field, the circuit comprising: aregulating circuit to reduce an offset variation of the output from themagnetic sensor elements arranged in the array, wherein the regulatingcircuit comprises a reference sensor element in the form of the magneticsensor element short-circuited between two output terminals.
 2. Themagnetic array sensor circuit as claimed in claim 1, wherein theregulating circuit comprises a storage element to store a sensor signalread out from the reference sensor element by selecting the sensorsignal as a reference offset value, and a subtraction circuit tosubtract the stored reference offset value from an output of the othermagnetic sensor elements, whereby an offset and drift of the magneticarray sensor circuit in its entirety are eliminated by this subtraction.3. The magnetic sensor array circuit as claimed in claim 2, whereinstorage of the offset value is carried out each time signals of one lineof the sensor array is read out to cancel a drift of the circuitresulting from change in environment.
 4. A magnetic array sensor circuitto process an output from a magnetic sensor array including a pluralityof magnetic sensor elements arranged in an array to detect a magneticfield, the circuit comprising: a regulating circuit for reducing anoffset variation of the output from the magnetic sensor elementsarranged in the array, wherein the regulating circuit includes a controlcircuit to operate the magnetic sensor element in a linear region,wherein the magnetic sensor elements are magnetic transistors, eachhaving two drain terminals, and wherein the control circuit causes themagnetic sensor elements to operate in the linear region whilerespective voltages at the two drain terminals of the magnetic sensorelement are rendered to be at the same potential.
 5. The magnetic sensorarray circuit as claimed in claim 4, wherein the control circuitcomprises a single-ended amplifier circuit and is configured so that anoffset within the amplifying circuit is compensated for by means of anoffset compensating circuit utilizing a switch and a capacitor.